1. Field of the Invention
The present invention generally relates to reading a memory device, and more particularly to a method and apparatus of generating the soft value for a memory device.
2. Description of the Prior Art
Flash memory is a non-volatile solid state memory device that can be electrically erased and reprogrammed, and is a specific type of electrically erasable programmable read-only memory (EEPROM) device. Data bit read out of a solid state memory such as the flash memory has a binary value, that is, “0” or “1,” which is commonly known as a hard value. However, the charge associated the data bit stored in the flash memory actually has an in-between value, which is commonly known as a soft value.
Error detection and correction is crucial in maintaining data reliability in a memory device such as the flash memory. This fact becomes more significant as either the density or the number of bits stored in each memory cell increases. Error correction code (ECC) is therefore commonly used to improve the reliability in the memory device.
The hard value of the read-out data is, nevertheless, insufficient or imprecise for detecting or correcting errors in the memory device. Therefore, a need has arisen to propose some schemes of generating the soft value that indicates the reliability or confidence of the read-out data from the memory device such as the flash memory. Accordingly, the generated soft value may be used to better estimate the in-between value of the stored charge, and be further used to effectively and precisely perform ECC decoding.